1. Field of the Invention
The present invention relates generally to devices used to interconnect and transfer forces between structural members such as the walls of a building and its roof framing system, and more particularly, to a strut system for providing direct, simplified and cost effective seismic connections that can articulate in three planes while transferring both tension and compression forces from the walls of new and existing concrete, concrete xe2x80x9ctilt-upxe2x80x9d and concrete block buildings to their diaphragm continuity elements.
2. Description of the Prior Art
Tilt-up buildings generally consist of those types of structures that are constructed with precast concrete wall panels that are precast horizontally on the ground, cured, and then tilted up into place. Concrete block walls are similar in character, but are built up block by block. Other concrete walls are typically cast in place.
The timber roof framing systems of older concrete, concrete tilt-up and concrete block buildings (hereinafter referred to generally as xe2x80x9cconcrete buildingsxe2x80x9d) that were built between the early to mid 1960""s were generally constructed with longspan timber roof trusses and timber roof joists. The timber trusses in these buildings were typically oriented to span the short direction of the building. Spacing between these trusses generally varies between 16 and 24 feet. The roof joists generally consist of 2xc3x978""s, 2xc3x9710""s, or 2xc3x9712""s spaced at 24xe2x80x3 o.c., and span between the timber trusses. At the perimeter of the building the roof joists span between the timber trusses and the walls, where they are typically framed onto a timber ledger that is bolted to the wall. Roof sheathing for these buildings typically consists of xe2x85x9cxe2x80x3 or xc2xdxe2x80x3 plywood.
After the mid 1960""s, the roof timber framing systems of most concrete as well as other types of buildings were generally constructed with glulam beams, instead of longspan timber trusses, and used a xe2x80x9cpanelizedxe2x80x9d roof framing system instead of roof joists. These modifications to the roof framing systems were typically made for economic reasons.
A xe2x80x9cpanelizedxe2x80x9d roof framing system consists of timber purlins, timber sub-purlins (also known as stiffeners), and roof sheathing. The roof sheathing typically consists of 4xe2x80x2xc3x978xe2x80x2 sheets of xe2x85x9cxe2x80x3 or xc2xdxe2x80x3 plywood, and spans between the sub-purlins. These sub-purlins are generally 2xc3x974""s or 2xc3x976""s, and span between the purlins. The purlins typically consist of 4xc3x9712""s or 4xc3x9714""s and span between the glulam beams (or in some cases longspan timber trusses). The plywood sheathing is typically oriented with it""s long dimension parallel to the sub-purlins, or perpendicular to the purlins. The sub-purlins are generally spaced 24xe2x80x3 apart. The purlins are typically spaced 8 feet apart to accommodate the length of the plywood sheathing. The glulam beams are typically spaced 20 to 24 feet apart. Sections of the panelized roof are typically fabricated on the ground and raised into place with a crane or forklift.
In buildings with timber framed roof diaphragms, the major roof framing elements, such as beams, girders, and trusses, are used as diaphragm continuity elements to form a plurality of spaced continuity lines that extend across the length and width of a building, i.e., a diaphragm continuity system. The purpose of a diaphragm continuity system is to provide a discrete structural system that provides for the transfer of seismic, wind, or other forces from the walls of a building into the roof diaphragm, and eventually to the structural elements intended to resist such forces. Forces from the walls are typically transferred to the diaphragm continuity elements through a sub-diaphragm. A sub-diaphragm is generally taken to be a localized area of the roof diaphragm that spans between diaphragm continuity elements and extends into the diaphragm a certain distance. This distance is dependent on the shear capacity of the sub-diaphragm and the forces that are to be transferred through the sub-diaphragm.
In areas subject to high seismicity, the connection between the walls of most older concrete buildings and their timber roof framing system is inadequate per the currently established seismic design standards for such buildings. Generally, this connection consists of only the nailing between the roof sheathing and the timber ledger that is bolted to the wall. This type of connection relies on a mechanism that subjects the ledgers to xe2x80x9ccross grain bendingxe2x80x9d, a mechanism that is highly vulnerable to failure. The deficiencies associated with this type of connection were responsible for numerous failures and collapses of concrete buildings during the 1971 San Fernando Earthquake. As a result, this type of connection has been specifically disallowed since the 1973 Edition of the Uniform Building Code. It is generally recommended that concrete buildings with such deficiencies be retrofitted with new connections per the currently established seismic design standards and/or recommendations for such buildings.
In some buildings constructed prior to the 1973 Edition of the uniform Building Code, and in most constructed afterwards, the walls of concrete, concrete tilt-up, and concrete block buildings are attached to the roof diaphragm, or sub-diaphragms, with discrete walls ties. Such wall ties generally consists of timber blocks or struts that are interconnected with metal straps, rods, holddown type connection devices, such as those disclosed in U.S. Pat. No. 5,249,404, or a combination thereof, and are only designed to resist tension forces, or may consist of the recently developed wall tie system disclosed in U.S. Pat. No. 5,809,719. These xe2x80x9cconventionalxe2x80x9d wall tie systems generally consist of many individual components that can take a significant amount of time to install, especially when the roof diaphragm is sloped (as is generally required for drainage, sometimes significantly) and the walls are not orthogonal to the diaphragm continuity elements. In many buildings, particularly older buildings with unblocked joisted non-panelized roof diaphragms, the sub-diaphragm shear capacity may be very limited, and require that those wall tie systems that rely on sub-diaphragms be extended from the wall into the roof diaphragm a significant distance in order to increase the depth of the sub-diaphragm, and hence reduce the sub-diaphragm shear stresses to within acceptable limits. Such conventional wall tie systems can be very costly.
It is therefore an object of the present invention to provide a simplified and cost effective seismic connection mechanism for transferring both tension and compression forces from the walls of buildings to their diaphragm continuity elements.
Another object of the present invention is to provide a seismic connection of the type described for connecting the walls of concrete buildings to diaphragm continuity elements consisting of the major roof framing elements such as beams, girders and trusses.
Yet another object of the present invention is to provide a seismic connection of the type described which is capable of transferring both tension and compression forces from building walls into the overall roof diaphragm through the beams, girders and/or trusses thereof.
Still another object of the present invention is to provide a seismic connection of the type described that eliminates dependence on the sub-diaphragm as a means of preserving wall to diaphragm integrity.
Briefly, a preferred embodiment of the present invention includes either a single or a plurality of strut pairs, each forming an assembly for transferring force between a wall and a roof diaphragm continuity element. Each assembly is comprised of two elongated strut elements, or load transfer members, each including a member at one end that allows longitudinal adjustment and rotation thereof, a first end connector assembly for facilitating connection of one end of the strut element to a wall, and a second end connector assembly for facilitating attachment of the other end of the strut element to a diaphragm continuity element connection assembly, the latter assembly being adapted to combine with a corresponding connection assembly and sandwich the continuity element therebetween. Each strut element is adapted to angularly intersect both the engaged wall and the diaphragm continuity element at angles which are determined by the particular buildings design.
An important advantage of the present invention is that it provides a reliable load transfer mechanism for use in structurally attaching the walls of new or existing tilt-up, concrete or concrete block wall buildings to their major roof framing elements.
Another advantage of the present invention is that it provides a simplified connection mechanism that can be used to connect walls and roof framing elements intersecting each other at any angle, either horizontally, vertically or both.
A further advantage is that it includes relatively lightweight components that can be manually installed without the use of heavy lifts, jacks, etc.